U.S. Pat. No. 3,556,392 discloses the production of water-soluble acrylamide polymers which are thermosetting by reason of a reactive content of glyoxal therein. These polymers are said to impart wet strength to paper when applied thereto and to possess the advantageous property of losing a part of said wet strength when said paper is soaked in water. While the ability of these wet-strength papers to lose their wet strength upon soaking in water is important, the more wet strength which can be lost, the better. The paper of said patent is disclosed as losing only 50% of its wet strength upon soaking in water at room temperature for 30 minutes. In order to the paper produced according to U.S. Pat. No. 3,556,392 to lose more than 50% of its wet strength, it is necessary that the water in which the paper is soaked be alkaline. However, it is of course highly improbable that water in which the paper is soaked by the consumer in the disposal of facial tissue, paper toweling, toilet tissue etc. will be alkaline. Therefore, efforts continue to develop polymeric systems which will impart temporary wet strength to paper but lose as much of that wet strength as possible upon exposure thereof to neutral water.
U.S. patent application Ser. No. 532,912, filed Aug. 16, 1983, now pending, discloses an improvement over the wet strength paper achieved by practicing the process of the above-referenced U.S. patent. This application discloses a polymeric system wherein a glyoxylated vinylamide polymer is reacted with a strong base at a pH of about 8.5 to 11 and thus requires an additional reaction over and above that required in the process of U.S. Pat. No. 3,556,392. The reaction with the strong base is very slow, oftimes consuming as many as 15-16 hours before complete.
Accordingly, the search for polymers which impart satisfactory wet strength to paper and still possess the ability to loss that wet strength upon soaking in neutral water at room temperature for short periods of time continues throughout the paper-making industry.